Conventionally, a fuel vapor processing system may recover fuel vapor, which is evaporated fuel from a fuel tank, and may supply the recovered fuel vapor into an intake air system of an internal combustion engine. A fuel vapor processing system may include a fuel vapor leakage detection device, which detects leakage of fuel vapor from a fuel tank and a canister. A fuel vapor leakage detection device may include a vane pump, a switching valve, a pressure sensor, and/or the like. The vane pump pressurizes or depressurizes an interior of a fuel tank and a canister. The switching valve switches between communication of the interior of the fuel tank and canister with the vane pump and communication of the interior of the fuel tank and canister with the atmosphere. The pressure sensor detects pressure in the fuel tank and the canister. Patent Document 1 may disclose a vane pump including a housing, a rotor, and a motor. The housing defines a pump chamber and has an intake hole and an exhaust hole, which communicate the pump chamber with the outside. The rotor is rotational in the pump chamber. The motor rotates the rotor. The intake hole and the exhaust hole are formed substantially at a center between an upper end surface and a lower end surface of the housing.